This invention relates to certain heterocyclocarbonyl- and acetyl-thiazolones, their use as cardiotonics in the treatment of heart failure, and their ability to enhance myocardial contractile force.
Heart failure is that physiological condition resulting from the inability of the ventricular myocardium to maintain adequate blood flow to the peripheral body tissues and includes congestive heart failure, backward and forward heart failure, right ventricular and left ventricular heart failure, and high-output and low-output heart failure. Heart failure can be caused by myocardial ischemia, myocardial infarction, excessive alcohol usage, pulmonary embolism, infection, anemia, arrhythmias, and systemic hypertension. Symptoms include tachycardia, fatigue with exertion, dyspnea, orthopnea and pulmonary edema.
Treatment involves either removal or correction of the underlying cause or involves control of the heart failure state. Management or control can be accomplished by increasing cardiac output or by decreasing cardiac work load. While work load can be reduced by reduction of physical activities and physical and emotional rest, increasing cardiac output has traditionally involved digitalis therapy. Digitalis stimulates contractile force of the heart which increases cardiac output and improves ventricular emptying. In this way, digitalis therapy normalizes venous pressure and reduces peripheral vasoconstriction, circulatory congestion and organ hypoperfusion.
Unfortunately, optimal doses of digitalis vary with the patient's age, size and condition and the therapeutic to toxic ratio is quite narrow. In most patients the lethal dose is only about five to ten times the minimal effective dose with toxic effects becoming apparent at only 1.5-2.0 times the effective dose. For these reasons, dose must be carefully tailored to suit the individual and frequent clinical examination and electrocardiogram is necessary to detect early signs of digitalis intoxication. Despite this care digitalis intoxication is reported in up to one-fifth of hospitalized patients undergoing therapy.
The need for less toxic cardiotonic agents is readily apparent. Applicants have discovered certain thiazolones which possess potent cardiotonic activity and by comparison to digitalis have fewer toxic effects.